The Vietnam War saw the birth of many new concepts in warfare. One of them was using helicopters in pairs as a scout and gunship. The scout helicopter was usually a modified troop-carrying Huey or Chinook in which rockets and machine guns had been added. The gunship was an attack Cobra helicopter with rockets, grenade launchers, and machine guns that provided support for the low-flying scout ships. Unfortunately, the low-flying scout helicopters, who frequently had gunners sitting or standing on the helicopters' skids, were excellent targets for enemy soldiers. A crewman on a scout helicopter did not have good odds of surviving his one-year tour in Vietnam.